Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Biological Sciences

First Advisor

David W. Foltz


Mussels representing two species (Mytilus trossulus and M. galloprovincialis) were collected from 28 littoral locations on the Pacific coast of the USA, and examined for genetic variation at 15 allozyme loci. Eleven samples from a region of suspected hybridization between the two species were also analyzed for variation in seven shell characters. Analysis of allozyme data by principal components analysis revealed three groups based on first principal component scores, and were identified as M. trossulus, M. galloprovincialis and hybrids. Canonical discriminate analysis of seven shell characters was less successful in separating mussels based on morphological criteria alone. To explore the possible effect of environmental variation on the distribution of M. trossulus and M. galloprovincialis, each sample location was characterized for four habitat characteristics: (1) temperature, (2) salinity, (3) tidal range and (4) degree of exposure to wave action which were used as independent variables in a series of multiple regression analyses with proportion of M. trossulus and M. galloprovincialis as dependent variables. Low temperature, temperature range, low salinity and salinity range had statistically significant effects on the proportion of M. trossulus at each location, while temperature range, low salinity and salinity range had statistically significant effects on the proportion of M. galloprovincialis at each location. Mytilus trossulus was more likely to occur at locations with lower temperatures and greater salinity variation than M. galloprovincialis. An ANOVA using a randomized complete block design was used to study the effect of tidal height on allele frequencies for a single allozyme locus, octopine dehydrogenase (Odh, E.C, Tidal height was determined not to have a significant effect on Odh allele frequencies for Mytilus in California, in contrast to a previous study of Mytilus populations in Europe where Odh allele frequencies varied significantly among samples from different tidal heights. In a separate study, an electrophoretic survey of a natural Mytilus trossulus population found ten active alleles for the octopine dehydrogenase (Odh) locus. A deficiency of heterozygous genotypes resulted in a statistically significant (P $<$ 0.005) departure from Hardy-Weinberg expectations. In vitro specific activity was determined for 207 mussels representing 17 different Odh genotypes. The Odh heterozygotes had an average specific activity 19% greater than that of homozygous genotypes (P $<$ 0.05).